PROPOSAL (Adapted from the applicant's abstract): About 20-30% of essential hypertensive patients will have less than the normal (15-20% of awake BP) decline in BP during sleep. This higher than normal sleep BP has been observed during ambulatory BP monitoring and such patients have been termed nondippers to distinguish them from patients with a normal sleep BP decline, dippers. Patients with nondipping sleep BP are continuously exposed to higher BP levels. This persistent hypertension is likely to be injurious to the endothelium and other organs susceptible to the ill effects of hypertension. Indeed, preliminary studies indicate that nondipper hypertensives have more evidence of hypertensive organ damage. The present study will, therefore, examine some important issues regarding the criteria for dipper and nondipper categories of BP, the reproducibility of such categorization and the effects of daytime and sleep activity on the decline of BP during sleep. The study will also compare sympathetic nervous system activity, salt sensitivity, and insulin resistance measures in relation to the extent of sleep BP reduction. Finally, endothelial function, retinal vascular structure and left ventricular mass will be compared in dippers and nondippers. The project will recruit 150 newly diagnosed and untreated hypertensive subjects to eliminate the effects of drug treatment on BP profiles. After an initial two-week period when the presence of hypertension will be confirmed by clinic BP readings, patients will undergo two separate 24-hour ambulatory BP and electronic activity monitoring sessions one to two weeks apart. During these two periods, awake and sleep sympathetic nervous system activity will be evaluated using plasma and urinary catecholamines. Sleep quality will be measured using a questionnaire and actigraphy derived indices of sleep quality. During the next two weeks and while remaining untreated, all patients will undergo endothelial function studies (B-mode ultrasound), retinal vascular structure assessment (high-resolution retinal photography), and left ventricular mass estimation (echocardiography). In the latter two years of the project, salt sensitivity and its relation to dipper and nondipper BP profiles will be studied. The reproducibility of the dipper and nondipper categorization will be examined in relation to the effects of sleep and daytime activity, sleep quality, and sympathetic nervous system activity. Direct comparisons between dipper and nondipper groups will be made in salt sensitivity, insulin resistance, and sympathetic nervous system activity. This study will provide information that will be important if clinical trials targeting nocturnal BP are to be designed.